In recent years, consideration has been given to a compression-ignition internal combustion engine typified by a homogeneous charge compression ignition engine in order to improve fuel consumption of internal combustion engines and to reduce emission. The compression-ignition internal combustion engine leads an oxygen containing gas and a fuel capable of compressed self-ignition into a cylinder and compressing the same for self-ignition.
It is, however, hard to control the ignition timing of the compression-ignition internal combustion engine, unlike a spark-ignition internal combustion engine. In addition, the compression-ignition internal combustion engine is susceptible to knocking in high required load of the compression-ignition internal combustion engine if a fuel of high ignitability is used and is susceptible to misfire in low required load of the compression-ignition internal combustion engine if a fuel of low ignitability is used. Therefore, the compression-ignition internal combustion engine has a problem of a narrow stable operating range.
To resolve the above problems, there is a conventionally known technology for supplying the compression-ignition internal combustion engine with a mixture of a fuel of high ignitability and a fuel of low ignitability provided therein (for example, refer to Japanese Patent Laid-Open No. 2001-355471). According to this technology, a stable operation is achieved in a wide range of required loads by adjusting the mixture ratio of the above fuels corresponding to the required load of the compression-ignition internal combustion engine. In this technology, however, the fuel of high ignitability and the fuel of low ignitability need be prepared individually and stored separately from each other.
On the other hand, there is also a known technology for using a single fuel to generate a ignitability suppressive substance by partially oxidizing a part of the fuel in the case of an increase in the required load of the compression-ignition internal combustion engine (for example, refer to Japanese Patent Laid-Open No. 2000-213444). Specifically, the technology is for use in generating a ignitability suppressive substance such as formaldehyde by partially oxidizing a part of hydrocarbon fuel such as light oil.
The technology, however, has a problem of requiring a high-temperature and long-term reaction to generate formaldehyde by partially oxidizing the hydrocarbon such as light oil.